Programmed cell death (PCD) refers to cell suicide that results from a genetically encoded program. Although widespread among multicellular organisms, there are relatively few documented instances of PCD in bacteria. In bacteria, PCD appears to have roles in limiting the spread of bacteriophage, and in the formation of biofilms. We have uncovered a potential PCD pathway in the pathogenic bacterium Pseudomonas aeruginosa. This PCD pathway can be activated in a subset of cells in response to DNA damage and promotes the virulence of P. aeruginosa in a lung infection model. DNA damage results in cleavage of an essential transcription regulator that we call AlpR, which leads to the activation of a cell lysis program via the de-repression of the alpA gene. In turn, AlpA positively regulates expression of the alpBCDE lysis genes. The cell lysis that ensues could provide nutrients or liberate toxins or other bacterial factors that might facilitate lung colonization by he remaining P. aeruginosa cells in the population. In Aim 1 we propose to determine how the AlpR-regulated alpBCDE genes influence cell lysis. In Aim 2 we propose to determine how AlpA positively controls the expression of target genes and identify an additional component of the PCD pathway that may be under the control of AlpA. Finally, in Aim 3 we will begin to determine how the PCD of a subset of P. aeruginosa cells in a population enhances virulence in an acute pneumonia model. With these studies we hope to elucidate how a pathogen exploits PCD as a survival-promoting strategy during the course of an infection. Additionally, our findings may have implications for the treatment of P. aeruginosa infections with antibiotics that damage the DNA.